(1) Field of the Invention
The present invention relates to a curable rubber composition comprising an ethylenically unsaturated nitrile/conjugated diene type highly saturated rubber composition. More particularly, an ethylenically unsaturated nitrile/conjugated diene type highly saturated rubber composition having an excellent strength and ozone resistance and is useful as the material for a belt, a roll or a hose.
(2) Description of the Related Art
The technique of improving the weatherability and heat resistance by incorporating a rubber having saturated bonds into a rubber having unsaturated bonds is well known.
For example, Japanese Unexamined Patent Publication No. 58-40332 teaches that a co-cured product obtained by curing a mixture of a partially hydrogenated unsaturated nitrile/conjugated diene type rubber and an ethylene/propylene copolymerrubber with sulfar by using a thiuram type accelerator or a dithiocarbamic acid type accelerator has an excellent heat resistance and weatherability. Moreover, Japanese Unexamined Patent Publication No. 61-40342 teaches that a product obtained by peroxidecuring a mixture comprising a substantially saturated hydrocarbon elastomer and a substantially saturated nitrile group-containing elastomer with a peroxide has an excellent thermal aging resistance and ethylene glycol resistance.
However, these rubbers have a problem in that, when they are used for belts, rolls and hoses, the strength is poor.
An ethylenically unsaturated nitrile/conjugated diene type highly saturated rubber has an excellent oil resistance and heat resistance, but this rubber has a poor ozone resistance and thus, cracking is caused by ozone contained in air. Therefore, various troubles occur when this rubber is applied to the above-mentioned uses. Accordingly, development of a rubber material having an excellent strength as well as an excellent heat resistance and ozone resistance has been desired.